1. Field of the Invention
The present invention relates to a transient electromagnetic field detector.
2. Description of the Prior Art
Electronic equipments are generally susceptible to even weak disturbing energy. Particularly, digital equipments such as a computer performing a high speed data processing are susceptible to such disturbing energy, whereby they are liable to malfunction. For example, logic elements commonly used in these digital equipments may cause logical inversion in response to a disturbing pulse of several nanoseconds, and these digital equipments are also sensible to the high frequency disturbing energy of 50 MHz-200 MHz. As sources of such transient disturbing energy, listed are noise caused by electrostatic discharge, noise at switching a power supply, and noise from a car engine which are so-called electromagnetic interference (EMI) sources, and particularly, noise components propagated by induction and radiation are regarded as important. For example, the instant a charged human body or utensil touches an equipment in operation, circuits may take such a logical state that cannot be expected to occur from the standpoint of design, thereby malfunctioning or stopping operation. Accordingly, it is necessary to work out an adequate countermeasure against such electromagnetic interference with its occurrence being presupposed in advance. At present, as an equipment for sensing and analyzing the presence of such EMI, a transient digitizer is known, but it is very expensive. An electric field strength meter, a power flux density meter, an EMI meter, and a spectrum analyzer are also known, but these instruments can merely measure continuous waves. Furthermore, a storage oscilloscope, a waveform memory, a memory voltmeter (or quasi-peak voltmeter), and a logic analyzer are also known, but these have had limitations in their measurable frequencies. Additionally, since, in these instruments, the conductive component of the disturbing energy was inevitably carried by signal cables and power cables connected to and from a measuring system, it was very difficult to measure the true radiation component separately. A high frequency electromagnetic field sensor for detecting transient electromagnetic fields causing such EMI has also been proposed, but this high frequency electromagnetic field sensor employs a dipole antenna having a length tuned to the frequency of an electromagnetic field to be detected, in accordance with the concept of a usual tuned antenna. Therefore, in order to detect the EMI of 50 MHz-200 MHz which is regarded as particularly important for digital equipments, the length of the antenna inevitably became several tens centimeters to one meter, and hence the whole sensor became large; further, also its measuring sensitivity varies in dependence on its tuned frequency and directivity; and therefore the sensor has not had a wide range of application.
In view of the above described prior art, it is an object of the present invention to provide a transient electromagnetic field detector which is inexpensive and of small size, whose sensitivity does not depend on the frequency, and which is broadly usable to detection and analysis of the electromagnetic interference.